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Abstract:

A method for detecting an analyze that may be present in ambient air,
bound to a surface or as part of complex aqueous media that includes
providing a metallole-containing polymer or copolymer, exposing the
polymer or copolymer to a suspected analyze or a system suspected of
including the analyze, and measuring a quenching of photoluminescence of
the metallole-containing polymer or copolymer exposed to the system. Also
included is a solid state inorganic-organic polymer sensor for detecting
nitroaromatic compounds that includes a substrate and a thin film of a
metallole-containing polymer or copolymer deposited on said substrate.

Claims:

1. A method for detecting an analyte that may be present in ambient air,
on a surface or as part of complex aqueous media comprising:providing a
metallole-containing polymer or copolymer;exposing said polymer or
copolymer to a suspected analyte or a system suspected of including the
analyte; andmeasuring a quenching of photoluminescence of said polymer or
copolymer exposed to said system.

2. The method of claim I further comprising selecting the polymer or
copolymer to be one of the group consisting of PDEBSi, PDEBGe, PDEBSF,
and PDEBGF.

3. The method of claim 1 wherein the polymer or copolymer is cast as a
thin film.

4. The method of claim 3 wherein the thin film is deposited on a solid
surface.

5. The method of claim 1 wherein the polymer or copolymer is sprayed onto
a solid surface having the analyte disposed thereon to form a thin film
of the polymer or copolymer on the solid surface.

6. The method of claim 5 wherein the solid surface comprises one of glass,
paper, metal, plastic, porcelain or wood.

7. The method of claim 1 wherein said step of exposing said polymer or
copolymer comprises submerging the polymer or copolymer in an aqueous
solvent.

8. The method of claim 1 wherein said step of exposing the polymer or
copolymer comprises submerging the polymer or copolymer in an organic
solvent.

9. The method of claim 1 wherein said step of measuring a quenching of
photoluminescence includes illuminating the polymer or copolymer with
light having a wavelength of between 250 nm and 420 nm and observing
photoluminescence quenching.

10. The method of claim 1 wherein said step of measuring a quenching of
photoluminescence includes subjecting said polymer or copolymer to
fluorescence spectrometry.

11. The method of claim 1 wherein the metallole-containing polymer or
copolymer is provided as an inorganic-organic polymer sensor that
comprises a substrate and a thin film of the metallole-containing polymer
or copolymer deposited on the substrate.

12. A solid-state inorganic-organic polymer sensor for detecting an
analyte comprising:a substrate; anda thin film of a metallole-containing
polymer or copolymer deposited on said substrate.

14. The sensor of claim 12 wherein said substrate is selected from the
group consisting of glass, paper, plastic, wood, porcelain, and metal.

15. The sensor of claim 12 wherein said metallole-containing polymer is
selected from the group consisting of PDEBSi, PDEBGe, PDEBSF, and PDEBGF.

16. A method of synthesizing inorganic-organic metallole-containing
polymers and copolymers comprising:obtaining dialkene or diyne;selecting
a catalyst; andconducting one of either hydrosilating the dialkene or
diyne with a dihydrosilole and hydrogermalating the dialkene or diyne
with a dihydrogermole.

17. The method of claim 16 wherein the catalyst is selected to be one from
the group consisting of H2PtCl6, Pd(PPh3)4, and
RhCl(PPh3).sub.3.

18. The method of claim 16 wherein the diyne is selected to be
diethynylbenzene, and wherein the diethynylbenzene is hydrosilated with a
dihydrosilole selected from the group consisting of
dihydro(tetraphenyl)silole and dihydrosilafluorene.

19. The method of claim 16 wherein the diyne is selected to be
diethynylbenzene, and wherein the diethynylbenzene is hydrogermalated
with a dihydrogermole selected from the group consisting of
dihydro(tetraphenyl)germole and dihydrogermafluorene.

20. A composition comprising an inorganic-organic metallole-containing
polymer or copolymer.

21. The composition of claim 20 wherein said inorganic-organic
metallole-containing polymer is synthesized via hydrosilation of a
dialkene or diyne with a dihydrosilole or a dihydrosilafluorene.

22. The composition of claim 20 wherein said metallole-containing polymer
is synthesized via hydrogermalation of a dialkene or diyne with a
dihydrogermole or a dihydrogermafluorene.

23. The composition of claim 20 wherein said metallole-containing polymer
comprises one of the group consisting of PDEBSi, PDEBGe PDEBSF, and
PDEBGF.

24. The composition of claim 20 wherein said metallole-containing polymer
or copolymer comprises a silafluorene-organic polymer.

25. The composition of claim 20 wherein said metallole-containing polymer
or copolymer comprises a germafluorene-organic polymer.

26. The composition of claim 20 wherein said metallole-containing polymer
or copolymer is a vinyl-bridged metallole polymer or copolymer.

Description:

TECHNICAL FIELD

[0001]A field of the invention is analyte detection. The instant invention
is directed to inorganic polymers and use of inorganic polymers, namely
photoluminescent metallole-containing polymers and copolymers, for
detection of nitroaromatic compounds based on photoluminescence
quenching.

BACKGROUND ART

[0002]Use of chemical sensors to detect ultra-trace analytes from
explosives has been the focus of investigation in recent years owing to
the critical importance of detecting explosives in a wide variety of
areas, such as mine fields, military bases, remediation sites, and urban
transportation areas Detecting explosive analytes also has obvious
applications for homeland security and forensic applications, such as the
examination of post-blast residue. Typically these chemical sensors are
small synthetic molecules that produce a measurable signal upon
interaction with a specific analyte.

[0003]Chemical sensors are preferable to other detection devices, such as
metal detectors, because metal detectors frequently fail to detect
explosives, such as in the case of the plastic casing of modern land
mines. Similarly, trained dogs are both expensive and difficult to
maintain. Other detection methods, such as gas chromatography coupled
with a mass spectrometer, surface-enhanced Raman, nuclear quadrupole
resonance, energy-dispersive X-ray diffraction, neutron activation
analysis and electron capture detection are highly selective, but are
expensive and not easily adapted to a small, low-power package.

[0004]Conventional chemical sensors have drawbacks as well. Sensing TNT
and picric acid in groundwater or seawater is important for the detection
of buried, unexploded ordnance and for locating underwater mines, but
most chemical sensor detection methods are only applicable to air samples
because interference problems are encountered in complex aqueous media.
Thus, conventional chemical sensors are inefficient in environmental
applications for characterizing soil and groundwater contaminated with
toxic TNT at military bases and munitions production and distribution
facilities. Also, conventional chemical sensors, such as highly
π-conjugated, porous organic polymers, are commonly used as chemical
sensors and can be used to detect vapors of electron deficient chemicals,
but require many steps to synthesize and are not selective to explosives.

[0005]Furthermore, many conventional chemical sensing methods are not
amenable to manufacture as inexpensive, low-power portable devices.
Additionally, these methods are limited to vapor phase detection, which
is disadvantageous given the low volatility of many explosives. For
example, the vapor pressure of TNT, which is approximately 5 ppb at room
temperature, may be up to six times lower when enclosed in a bomb or mine
casing, or when present in a mixture with other explosives.

[0006]Additionally, current routes for synthesis of polymetalloles use
hazardous reagents and are of low efficiency. For example,
poly(tetraphenyl)silole has been synthesized by Wurtz-type
polycondensation, but the reaction yields are low.

DISCLOSURE OF INVENTION

[0007]An embodiment of the present invention is a directed device and
method for detecting solid-state, vapor phase and solution phase
nitroaromatic compounds using an inorganic polymer sensor, namely
photoluminescent metallole-containing polymers and copolymers. The
invention also includes a method for synthesizing an inorganic polymer
sensor, namely photoluminescent metallole-containing copolymers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a model of a polysilole molecule;

[0009]FIG. 2 illustrates a pair of equations for the synthesis of
polygermole and polysilole according to an embodiment of the invention;

[0010]FIG. 3 illustrates a pair of equations for the synthesis of a
silole-germole copolymer according to an embodiment of the invention;

[0011]FIG. 4 illustrates a pair of equations for the synthesis of
silole-silane alternating copolymers according to an embodiment of the
invention;

[0012]FIG. 5 is a table of the absorption and fluorescence spectra
observed in one embodiment of the instant invention and taken at the
concentrations of 2 mg/L in THF and 10 mg/L in toluene, respectively;

[0021]FIG. 14 illustrates a structure of the pentiptycene-derived polymer;

[0022]FIG. 15 illustrates, from left to right, highest and lowest
photoluminescence quenching efficiency for picric acid (left-most two
lines), TNT (two lines immediately to the right of picric acid), DNT (two
lines immediately to the right of TNT), and nitrobenzene (right-most two
lines) showing how the varying polymer response to analyte could be used
to distinguish analytes from each other;

[0023]FIG. 16 illustrates a comparison of the photoluminescence quenching
constants (from Stern-Volmer plots) of polymers 1-12 with different
nitroaromatic analytes;

[0025]FIG. 18 illustrates a schematic diagram of electron-transfer
mechanism for quenching the photoluminescence of polymetallole by
analyte;

[0026]FIG. 19 illustrates an absence of quenching of photoluminescence by
polysilole 1 with 4 parts per hundred of THF; and

[0027]FIG. 20 illustrates an equation for a catalytic dehyrdocoupling
method for synthesizing metallole polymers according to one embodiment of
the invention.

[0028]FIGS. 21a, 21b and 21c illustrate various copolymers as well as
their syntheses, namely PDEBSi, PDEBGe, PDEBSF, PDEBGF, PSF and PGF;

[0029]FIG. 22 is a table summarizing the detection limits of TNT, DNT, and
picric acid using the five metallole-containing polymers synthesized,
PSi, PDEBSi, PGe, PDEBGe, and PDEBSF;

[0030]FIG. 23 are black and white images of the luminescence quenching of
three polymers, PSi, PDEBSi, and PGe, by 200, 100, 50, and 10 ng TNT on
porcelain plates as observed on a porcelain plate; and

[0031]FIG. 24 are exemplary black and white images of the luminescence
quenching of polysilole by each analyte at different surface
concentrations.

BEST MODE FOR CARRYING OUT THE INVENTION

[0032]Solid state sensing may be especially desirable for trace residue
detection on surfaces believed to be contaminated, such as, for example,
where filter paper is used to swab or wipe a surface of interest and the
filter paper is subsequently subjected to analysis. Conventional solid
state detection kits, such as that manufactured under the brand name
ExPray® by Plexus Scientific Corporation of Alexandria, Va. are able
to detect various explosive through a color change, with sensitivity down
to the tens of nanogram level.

[0033]The vapor pressure of TNT, for example, which is approximately 5 ppb
at room temperature, may be up to 6 times lower when enclosed in a bomb
or mine casing or when present in mixtures with other explosives.
Accordingly, embodiments of the invention include the solid-state
detection of trace residue of nitroaromatics, such as picric acid (PA,
2,4,6-trinitrophenol or C6H2(NO2)3OH), nitrobenzene
(NB or C6H5NO2), 2,4-dinitrotoluene (DNT or
C7H6N2O4) and 2,4,6-trinitrotoluene (TNT or
C7H5N3O6), using thin films of luminescent
metallole-containing polymers. Advantageously, detection limits as low as
5 ng are obtained. Polymetalloles and copolymers have the advantage of
being inexpensive, easily prepared, and readily fielded for on-site
explosives detection.

[0034]For example, one preferred embodiment includes a method for
detecting an analyte that may be present in ambient air, bound to a
surface or as part of complex aqueous media that includes a
metallole-containing polymer or copolymer being exposed to a system
suspected of containing the analyte, such as on a solid surface or in an
aqueous medium. By subsequently measuring the photoluminescence of the
metallole-containing polymer or copolymer, the presence, absence and
approximate quantity may be determined with great sensitivity. By
illuminating the polymer or copolymer with light having a wavelength of
between 250 nm and 420 nm, photoluminescence quenching may be observed.

[0035]Another preferred embodiment includes a metallole-containing polymer
sensor for sensing trace amounts of nitroaromatic compounds that includes
a metallole-containing polymer cast, sprayed or otherwise deposited on a
surface suspected of containing the nitroaromatic compounds. It is
contemplated that the solid surface on which detection may occur may
include a virtually boundless number of surfaces, such as glass, paper,
plastic, wood, porcelain or metal, to name a few.

[0036]Additionally, embodiments of the invention include the synthesis and
use of inorganic polymers, namely photoluminescent metallole-containing
polymers and copolymers, in solid state or solution for detection of
nitroaromatic compounds based on photoluminescence quenching.
Inorganic-organic polymers may be prepared by catalytic hydrosilation or
hydrogermylation with dihydrosilole or dihydrogermole compounds and
organic diynes or dialkenes. The invention includes an inexpensive and
highly efficient inorganic or inorganic-organic polymer sensor that can
detect the existence of an analyte, namely nitroaromatic compounds such
as picric acid, nitrobenzene, DNT and TNT in air, water, on surfaces,
organic solution, or other complex aqueous media.

[0037]Photoluminescent metallole polymers are stable in air, water, acids,
common organic solvents, and even seawater containing bioorganisms.
Therefore, the inorganic polymer sensor of the instant invention includes
the metallole copolymers for detection of analytes in these media.
Importantly, the inorganic polymer sensors of the instant invention are
insensitive to organic solvents and common environmental interferents,
allowing the use of the sensor in a wide variety of environments and
applications.

[0038]Metalloles are silicon (Si) or germanium (Ge)-containing
metallocyclopentadienes that include one-dimensional Si--Si, Ge--Ge, or
Si--Ge wires encapsulated with highly conjugated organic ring systems as
side chains. Silole and germole dianions (RC)4Si2- and
(RC)4Ge2-, where R=Ph or Me, have been studied by X-ray
crystallography and found to be extensively delocalized. Siloles and
germoles are of special interest because of their unusual electronic and
optical properties, and because of their possible application as electron
transporting materials in devices. Polysilanes and polygermanes
containing a metal-metal backbone emit in the near UV spectral region,
exhibit high hole mobility, and show high nonlinear optical
susceptibility, which makes them efficient photoemission candidates for a
variety of optoelectronics applications. These properties arise from a
σ-σ* delocalization along the M-M backbones and confinement
of the conjugated electrons along the backbone.

[0039]Polymetalloles and metallole-silane copolymers are unique in having
both a M-M backbone as well as an unsaturated five-membered ring system.
These polymers are highly photoluminescent, and are accordingly useful as
light emitting diodes (LEDs) or as chemical sensors. Characteristic
features of polymetalloles and metallole-silane copolymers include a low
reduction potential and a low-lying lowest unoccupied molecular orbital
(LUMO) due σ*-π* conjugation arising from the interaction
between the σ* orbital of silicon or germanium and the π*
orbital of the butadiene moiety of the five membered ring. In addition,
the M-M backbones exhibit (σ*-σ* delocalization, which
further delocalizes the conjugated metallole X electrons along the
backbone. Electron delocalization in these polymers provides a means of
amplification, because interaction between an analyte molecule and any
position along the polymer chain is communicated throughout the
delocalized chain.

[0040]Detection may be accomplished by measurement of the quenching of
photoluminescence of metallole copolymers by the analyte. Sensitivity of
metallole copolymers to the analytes picric acid, TNT, DNT and NB is as
follows: PA>TNT>DNT>NB. A plot of log K versus the reduction
potential of analytes (NB, DNT, and TNT) for each metallole copolymer
yields a linear relationship, indicating that the mechanism of quenching
is attributable to electron transfer from the excited metallole
copolymers to the lowest unoccupied orbital of the analyte.

[0041]Excitation may be achieved with electrical or optical stimulation.
If optical stimulation is used, a light source containing energy that is
larger than the wavelength of luminescence emission of the polymer is
preferably used. This could be achieved with, for example, a mercury
lamp, a blue light emitting diode, or an ultraviolet light emitting
diode.

[0042]FIG. 1 illustrates a space filling model structure of polysilole 1,
which features a Si--Si backbone inside a conjugated ring system of side
chains closely packed to yield a helical arrangement. FIG. 2 illustrates
polymers 1 and 2, FIG. 3 illustrates polymer 3, and FIG. 4 illustrates
copolymers 4-12. FIGS. 21a through 21c illustrate additional copolymers
as well as their syntheses,
Poly(1,4diethynylbenzene)2,3,4,5-tetraphenylsilole (PDEBsilole), Poly(
1,4-diethynylbenzene)2,3,4,5-tetraphenylgermole (PDEBgermole),
Poly(1,4-diethynylbenzene)silafluorene (PDEBSF),
Poly(1,4-diethynylbenzene)germafluorene (PDEBGF), Polysilafluorene (PSF)
and Polygermafluorene (PGF). A similar means of amplification is
available to quantum-confined semiconductor nanocrystallites, via a
three-dimensional crystalline network, where the electron and hole wave
functions are delocalized throughout the nanocrystal.

[0043]A conventional method for preparing polymetalloles and metallole
copolymers is Wurtz-type polycondensation. The syntheses of polygermole
and polysiloles, and other copolymers are analogous to one another, as
illustrated in equation 1 in FIG. 2, and employ the Wurtz-type
polycondensation. However, yields from this method of synthesis are low
(ca. ˜30%). Thus, Wurtz-type polycondensation is not well-suited to
large-scale production.

[0044]Embodiments of the instant invention include alternative methods for
synthesizing polymetalloles that use catalytic dehydrocoupling of
dihydrosiloles with a catalyst as an attractive alternative to Wurtz-type
polycondensation. Bis(cyclopentadienyl) complexes of Group 4 have been
extensively studied and shown to catalyze the dehydrocoupling of
hydrosilanes to polysilanes for the formation of Si--Si bonds. However,
only the primary organosilanes react to give polysilane. Secondary and
tertiary silanes give dimers or oligomers in low yield. It has been
reported that the reactivity decreases dramatically with increasing
substitution at the silicon atom, since reactions catalyzed by
metallocenes are typically very sensitive to steric effects. Mechanisms
for dehydrogenative coupling of silanes have also been extensively
investigated, which involves σ-bond metathesis.

[0045]Embodiments of the instant invention include catalytic
dehydrocoupling of dihydrosiloles and dihydrogermoles with a catalyst. In
one embodiment, the invention includes catalytic dehydrocoupling
polycondensation of dihydro(tetraphenyl)silole or
dihydro(tetraphenyl)germole with 1-5 mol % of Wilkinson's catalyst,
Rh(PPh3)3Cl, or Pd(PPh3)4, as illustrated in FIG. 2,
or 0.1-0.5 mol % of H2PtCl6.xH2O in conjunction with 2-5
equivalents of allylamine, or other alkene, such as cyclohexene, for
example, as illustrated in FIG. 20. The latter reactions produce the
respective polysilole or polygermole in high yield (ca. 80-90%). By
1H NMR spectroscopy, the monomer, dihydrometallole, was completely
consumed in the reaction. Molecular weights (Mw) of 4000-6000 are
obtained, similar to those obtained by the Wurtz-type polycondensation
(ca. ˜30%).

[0046]Turning now to FIG. 3, silole-germole alternating copolymer 3, in
which every other silicon or germanium atom in the polymer chain is also
part of a silole or germole ring, was synthesized from the coupling of
dichloro(tetraphenyl)germole and dilithio(tetraphenyl)silole. The latter
is obtained in 39% yield from dichlorotetraphenylsilole by reduction with
lithium, as illustrated in the equation of FIG. 3. The molecular weight
of the silole-germole copolymer, Mw=5.5×103,
Mn=5.0×103 determined by SEC (size exclusion
chromatography) with polystyrene standards, is similar to that of
polysiloles or polygermoles. All of the polymetalloles are extended
oligomers with a degree of polymerization of about 10 to 16, rather than
a true high Mw polymer; however, they can be cast into a thin film
from solution and show polymer-like properties.

[0047]Also illustrated in FIG. 4 are silole-silane alternating copolymers
4, 5, 6, 7, 8, which were also prepared from coupling of the silole
dianion (Ph4C4Si)Li2 with the corresponding silanes.
Germole-silane alternation copolymers 9, 10, 11, 12 were also synthesized
from the coupling of the germole dianion (Ph4C4Ge)Li2 with
the corresponding silanes, as illustrated in FIG. 4. These reactions
generally employ reflux conditions in tetrahydrofuran under an argon
atmosphere for about 72 hours. Some silole-silane copolymers have been
synthesized previously and shown to be electroluminescent.
Metallole-silane copolymers were developed so that they could be easily
functionalized along the backbone by hydrosilation. The molecular weight
of metallole-silane copolymers,
Mw=4.1×103˜6.2×103,
Mn=4.1×103˜5.4×103 determined by SEC, is
similar to that of the polymetalloles.

[0049]Inorganic-organic poly(1,4-diethynylbenzene)metallole (DEB) type
polymers may be obtained by hydrosilation of an dialkyne, specifically
DEB, with a dihydrometallole using a catalyst such as chloroplatinic
acid. FIGS. 21a-21c illustrate the reaction whereby the DEB type polymers
are obtained according to embodiments of the invention. A reasonable
extension of this principle includes hydrosilation and hydrogermylation
of any organic diyne. A reasonable interpolation of this principle
includes hydrosilation and hydrogermylation of organic dialkenes to
obtain less conjugated polymers.

Absorption And Fluorescence

[0050]The UV-vis absorption and fluorescence spectral data for polymers
1-12 are also illustrated in Table 1 of FIG. 5. The
poly(tetraphenyl)metalloles 1-3 and tetraphenylmetallole-silane
copolymers 4-12 exhibit three absorption bands, which are ascribed to the
π-π* transition in the metallole ring and the
σ-(σ*+π*) and σ-σ* transitions in the M-M
backbone. FIG. 6 illustrates a schematic energy-level diagram for
polymetalloles and metallole-silane copolymers.

[0051]UV-vis absorption in THF (solid line) and fluorescence spectra in
toluene (dotted line) for poly(tetraphenygermole) 2, silole-silane
copolymer 4 and germole-silane copolymer 9 are shown in FIG. 7.
Absorptions at a wavelength of about 370 nm for the
poly(tetraphenylmetallole)s 1-3 and tetraphenylmetallole-silane
copolymers 4-12 are ascribed to the metallole π-π* transition of
the metallole moiety, which are about 89 to 95 nm red-shifted relative to
that of oligo[1,1-(2,3,4,5-tetramethylsilole)] (λmax=275 nm)
and are about 75 to 81 nm red-shifted relative to that of
oligo[1,1-(2,5-dimethyl-3,4-diphenylsilole)] (λmax=289 nm).
These red shifts are attributed to an increasing main chain length and
partial conjugation of the phenyl groups to the silole ring.

[0052]FIG. 8 shows the HOMO (A) and LUMO (B) of 2,5-diphenylsilole,
Ph2C4SiH2, from the ab initio calculations at the HF/6-31G* level. Phenyl
substituents at the 2,5 metallole ring positions may π-conjugate with
the metallole ring LUMO. Second absorptions at wavelengths of 304 to 320
nm for the poly(tetraphenylmetallole)s 2-3 and
tetraphenylmetallole-silane copolymers 4-12 are assigned to the
σ-(σ2*+π*) transition, which parallels that of the
poly(tetraphenyl)silole 1.

[0053]Polymetallole 1-2 and silole-silane copolymers 4-7 exhibit one
emission band (λmax, 486 to 513 nm) when excited at 340 nm,
whereas the others exhibit two emission bands with λmax of
480-510 nm and 385-402 nm. The ratios of the two emission intensities are
not concentration dependent, which indicates that the transition does not
derive from an excimer. Emission peaks for germole-silane copolymers 9-12
are only 2 to 33 nm blue-shifted compared to the other polymers. FIG. 9
shows fluorescence spectra of the poly(tetraphenyl)silole in toluene
solution (solid line) and in the solid state (dotted line). The bandwidth
of the emission spectrum in solution is slightly larger than in the solid
state. There is no shift in the maximum of the emission wavelength. This
suggests that the polysilole exhibits neither π-stacking of polymer
chains nor excimer formation.

[0054]The angles of C-M-C of dihydro(tetraphenyl)silole and
dihydro(tetraphenyl)germole are 93.11° on C--Si--C and 89.760 on
C--Ge--C, respectively. Polymerization might take place, since the
tetraphenylmetalloles have small angles at C-M-C in the
metallocyclopentadiene ring, which results in less steric hindrance at
the metal center. In addition, the bulky phenyl groups of silole might
prevent the formation of cyclic hexamer, which is often problematic in
polysilane syntheses. Cyclic polymetallole product formation was not
observed.

Fluorescence Quenching With Nitroaromatic Analytes

[0055]The method of detection of the instant invention includes using a
chemical sensor, namely a variety of photoluminscent copolymers having a
metalloid-metalloid backbone such as Si--Si, Si--Ge, or Ge--Ge, or
alternatively an inorganic-organic metallole-containing copolymer. While
polymetalloles in various forms may be used to detect analytes, one
embodiment includes casting a thin film of the copolymers is employed in
detecting the analyte, e.g., picric acid, DNT, TNT and nitrobenzene.
Detection is achieved by measuring the quenching of the photoluminescence
of the copolymer by the analyte. Accordingly, the instant invention
contemplates use of the polymetallole polymers and copolymers in any form
susceptible to measurement of photoluminescence quenching. For example,
since it is possible to measure fluorescence of solutions, other
embodiments of the instant method of detection may optionally include a
polymetallole in solution phase, where powdered bulk polymer is dissolved
in solution. Yet another embodiment includes producing a colloid of the
polymer, which is a liquid solution with the polymer precipitated and
suspended as nanoparticles.

[0056]The detection method involves measurement of the quenching of
photoluminescence of the polymetalloles 1-3 and metallole-silane
copolymers 4-12 by the analyte, such as a toluene solution (using a
Perkin-Elmer LS 50B fluorescence spectrometer, 340 nm excitation
wavelength). For example, turning now to FIG. 10, when used to detect
TNT, fluorescence spectra of a toluene solution of the metallole
copolymers were obtained upon successive addition of aliquots of TNT.
Photoluminescence quenching of the polymers 1-12 in toluene solutions
were also measured with nitrobenzene, DNT, TNT and nitrobenzene. The
relative efficiency of photoluminescence quenching of metallole
copolymers is unique for TNT, DNT, and nitrobenzene, respectively, as
indicated in FIG. 10 by the values of K determined from the slopes of the
steady-state Stern-Volmer plots. FIG. 10 demonstrates that each copolymer
has a unique ratio of quenching efficiency to the corresponding analyte.

[0057]The purity of the TNT sample was found to be important to obtain
reproducible results. It was synthesized by nitration of dinitrotoluene
and recrystallized twice from methanol. A third recrystallization
produces the same results as the twice-recrystallized material. When the
quenching experiment was undertaken without recrystallization of TNT,
higher (ca. 10×) quenching percentages are obtained. Presumably,
impurities with higher quenching efficiencies are present in crude TNT.

[0058]The Stern-Volmer equation, which is (Io/I)-1=Ksv[A], is
used to quantify the differences in quenching efficiency for various
analytes. In this equation, Io is the initial fluorescence intensity
without analyte, and I is the fluorescence intensity with added analyte
of concentration [A], and Ksv is the Stern-Volmer constant.

[0059]FIG. 11 shows the Stern-Volmer plots of polysilole 1, polygermole 2,
and silole-silane copolymer 8 for each analyte. A linear Stern-Volmer
relationship was observed in all cases, but the Stern-Volmer plot for
picric acid exhibits an exponential dependence when its concentration is
higher than 1.0×10-4 M. A linear Stern-Volmer relationship may
be observed if either static or dynamic quenching process is dominant.
Thus, in the case of higher concentrations of picric acid, the two
processes may be competitive, which results in a nonlinear Stern-Volmer
relationship. This could also arise from aggregation of analyte with
chromophore.

[0060]Photoluminescence may arise from either a static process, by the
quenching of a bound complex, or a dynamic process, by collisionally
quenching the excited state. For the former case, Ksv is an
association constant due to the analyte-preassociated receptor sites.
Thus, the collision rate of the analyte is not involved in static
quenching and the fluorescence lifetime is invariant with the
concentration of analyte. With dynamic quenching, the fluorescence
lifetime should diminish as quencher is added.

[0061]A single "mean" characteristic lifetime (τ) for polymetalloles
and metallole-silane copolymers 1-12 has been measured and summarized in
Table 1 of FIG. 5. Luminescence decays were not single-exponential in all
cases. Three lifetimes were needed to provide an acceptable fit over the
first few nanoseconds. The amplitudes of the three components were of
comparable importance (the solvent blank made no contribution). These
features suggest that the complete description of the fluorescence is
actually a continuous distribution of decay rates from a heterogeneous
collection of chromophore sites. Because the oligomers span a size
distribution, this behavior is not surprising. The mean lifetime
parameter reported is an average of the three lifetimes determined by the
fitting procedure, weighted by their relative amplitudes. This is the
appropriate average for comparison with the "amount" of light emitted by
different samples under different quenching conditions, as has been
treated in the literature. Given this heterogeneity, possible long-lived
luminescence that might be particularly vulnerable to quenching has been
a concern. However, measurements with a separate nanosecond laser system
confirmed that there were no longer-lived processes other than those
captured by the time-correlated photon counting measurement and
incorporated into Table 1 of FIG. 5.

[0062]It is notable that polysilole 1 and silole-silane copolymers 4-8
have about 3 to 11 times longer fluorescence lifetimes than polygermole 2
and germole-silane copolymers 9-12. Fluorescence lifetimes in the thin
films (solid state) for polysilole 1 and polygermole 2 are 2.5 and 4.2
times longer than in toluene solution, respectively. The fluorescence
lifetimes as a function of TNT concentration were also measured and are
shown in the inset of FIG. 11 for polymers 1, 2, and 8. No change of mean
lifetime was observed by adding TNT, indicating that the static quenching
process is dominant for polymetalloles and metallole-silane copolymers
1-12 (FIG. 12). Some issues with such analyses have been discussed in the
literature. This result suggests that the polymetallole might act as a
receptor and a TNT molecule would intercalate between phenyl substituents
of the metallole moieties (FIG. 1).

[0063]For chemosensor applications, it is useful to have sensors with
varied responses. Each of the 12 polymers exhibits a different ratio of
the photoluminescence quenching for picric acid, TNT, DNT, and
nitrobenzene and a different response with the same analyte. The use of
sensor arrays is inspired by the performance of the olfactory system to
specify an analyte. FIG. 13 displays the Stern-Volmer plots of polymers
1, 2, 4, 5, and 6 for TNT, indicating that the range of photoluminescence
quenching efficiency for TNT is between 2.05×103 and
4.34×103 M-1. The relative efficiencies of
photoluminescence quenching of poly(tetraphenylmetallole)s 1-3 and
tetraphenyl-metallole-silane copolymers 4-12 were obtained for picric
acid, TNT, DNT, and nitrobenzene, as indicated by the values of Ksv
determined from the slopes of the steady-state Stern-Volmer plots and
summarized in Table 1 of FIG. 5. Polymer 13, which is illustrated in FIG.
14, is an organic pentiptycene-derived polymer for comparison. The
metallole copolymers are more sensitive to TNT than the organic
pentiptycene-derived polymers in toluene solution. For example,
polysilole 1 (4.34×103 M-1) has about a 370% better
quenching efficiency with TNT than organic pentiptycene-derived polymer
(1.17×103 M-1).

[0064]The trend in Stern-Volmer constants usually reflects an enhanced
charge-transfer interaction from metallole polymer to analyte. For
example, the relative efficiency of photoluminescence quenching of
polysilole 1 is about 9.2:3.6:2.0:1.0 for picric acid, TNT, DNT, and
nitrobenzene, respectively. Although polysilole 1 shows best
photoluminescence quenching efficiency for picric acid and TNT, polymer 9
and 5 exhibit best quenching efficiency for DNT and nitrobenzene,
respectively. (FIG. 15) Polygermole 2 has the lowest quenching efficiency
for all analytes. Since the polymers 1-12 have similar molecular weights,
the range of quenching efficiencies with the same analyte would be
expected to be small. Polysilole 1 (11.0×103 M-1 and
4.34×103 Me-1) exhibits 164% and 212% better quenching
efficiency than polygermole 2 (6.71×103 M-1 and
2.05×103 M-1) with picric acid and TNT, respectively.
Polymer 9 (2.57×103 M-1) has 253% better quenching
efficiency than polymer 2 (1.01×103 M-1) with DNT.
Polymer 5 (1.23×103 M-1) has 385% better quenching
efficiency than metallole polymer 2 (0.32×103 M-1) with
nitrobenzene. FIG. 16 illustrates how an analyte might be specified using
an array of multi-sensors.

[0065]FIG. 17 shows a plot of log Ksv vs. reduction potential of analytes.
All metallole polymers exhibit a linear relationship, even though they
have different ratios of photoluminescence quenching efficiency to
analytes. This result indicates that the mechanism of photoluminescence
quenching is primarily attributable to electron transfer from the excited
metallole polymers to the LUMO of the analyte. Because the reduction
potential of TNT (-0.7 V vs NHE) is less negative than that of either DNT
(-0.9 V vs NHE) or nitrobenzene (-1.15 V vs NHE), it is detected with
highest sensitivity. A schematic diagram of the electron-transfer
mechanism for the quenching of photoluminescence of the metallole
polymers with analyte is shown in FIG. 18. Optical excitation produces an
electron-hole pair, which is delocalized through the metallole
copolymers. When an electron deficient molecule, such as TNT is present,
electron-transfer quenching occurs from the excited metallole copolymer
to the LUMO of the analyte. The observed dependence of Ksv on analyte
reduction potential suggests that for the static quenching mechanism, the
polymer-quencher complex luminescence intensity depends on the electron
acceptor ability of the quencher. An alternative explanation would be
that the formation constant (Ksv) of the polymer-quencher complex is
dominated by a charge-transfer interaction between polymer and quencher
and that the formation constant increases with quencher electron acceptor
ability.

[0066]An important aspect of the metallole copolymers is their relative
insensitivity to common interferents. Control experiments using both
solutions and thin films of metallole copolymers (deposited on glass
substrates) with air displayed no change in the photoluminescence
spectrum. Similarly, exposure of metallole copolymers both as solutions
and thin films to organic solvents such as toluene, THF, and methanol or
the aqueous inorganic acids H2SO4 and HF produced no
significant decrease in photoluminescence intensity. FIG. 19 shows that
the photoluminescence spectra of polysilole 1 in toluene solution display
no quenching of fluorescence with 4 parts per hundred of THF. The ratio
of quenching efficiency of polysilole 1 with TNT vs benzoquinone is much
greater than that of polymer 13. The Ksv value of 4.34×103
M-1 of polysilole 1 for TNT is 640% greater than that for
benzoquinone (Ksv=674 M-1)-1 The organic polymer 13, however,
only exhibits a slightly better quenching efficiency for TNT
(Ksv=1.17×103 M-1) (ca. 120%) compared to that (Ksv=998
M-1) for benzoquinone. This result indicates that polysilole 1
exhibits less response to interferences and greater response to
nitroaromatic compounds compared to the pentiptycene-derived polymer 13.

[0069]This corresponds to an extrapolated detection limit of ˜1.5
ppt for instant detection with our fluorescence spectrometer at the 95%
confidence limit. Of course, this is for solution data and with a
spectrometer, which is not optimized for detection at a single
wavelength.

EXAMPLE

[0070]All synthetic manipulations were carried out under an atmosphere of
dry dinitrogen gas using standard vacuum-line Schlenk techniques. All
solvents were degassed and purified prior to use according to standard
literature methods: diethyl ether, hexanes, tetrahydrofuran, and toluene
purchased from Aldrich Chemical Co. Inc. were distilled from
sodium/benzophenone ketal. Spectroscopic grade of toluene from Fisher
Scientific was used for the fluorescent measurement. NMR grade
deuteriochloroforrn was stored over 4 Å molecular sieves. All other
reagents (Aldrich, Gelest) were used as received or distilled prior to
use. NMR data were collected with Varian Unity 300, 400, or 500 MHz
spectrometers (300.1 MHz for 1H NMR, 75.5 MHz for 13C NMR and
99.2 MHz for 29Si NMR) and all NMR chemical shifts are reported in
parts per million (δ ppm); downfield shifts are reported as
positive values from tetramethylsilane (TMS) as standard at 0.00 ppm. The
1H and 13C chemical shifts are reported relative to CHCI3
(δ 77.0 ppm) as an internal standard, and the 29Si chemical
shifts are reported relative to an external TMS standard.

[0071]NMR spectra were recorded using samples dissolved in CDCl3,
unless otherwise stated, on the following instrumentation. 13C NMR
were recorded as proton decoupled spectra, and 29Si NMR were
recorded using an inverse gate pulse sequence with a relaxation delay of
30 seconds. The molecular weight was measured by gel permeation
chromatography using a Waters Associates Model 6000A liquid chromatograph
equipped with three American Polymer Standards Corp. Ultrastyragel
columns in series with porosity indices of 103, 104, and
105 Å, using freshly distilled THF as eluent.

[0072]The polymer was detected with a Waters Model 440 ultraviolet
absorbance detector at a wavelength of 254 nm, and the data were
manipulated using a Waters Model 745 data module. Molecular weight was
determined relative to calibration from polystyrene standards.
Fluorescence emission and excitation spectra were recorded on a
Perkin-Elmer Luminescence Spectrometer LS 50B. Monomers,
1,1-dichloro-2,3,4,5-tetraphenylsilole,
1,1-dichloro-2,3,4,5-tetraphenylgermole,
1,1-dilithio-2,3,4,5-tetraphenylsilole, and
1,1-dilithio-2,3,4,5-tetraphenylgermole were synthesized by following the
procedures described in the literature. All reactions were performed
under Ar atmosphere.

[0073]Polymetalloles 1, 2, and 3 were synthesized by following the
procedures described in the literature.

Preparation of Silole-Silane Copolymers, (Silole-SiR1R2)

[0074]Stirring of 1,1-dichloro-2,3,4,5-tetraphenylsilole (5.0 g, 11.0
mmol) with lithium (0.9 g, 129.7 mmol) in TEF (120 mL) for 8 h at room
temperature gave a dark yellow solution of silole dianion. After removal
of excess lithium, 1 mol equiv of corresponding silanes,
R1R2SiCl2(11.0 mmol) was added slowly to a solution of
tetraphenylsilole dianion, and stirred at room temperature for 2 hours.
The resulting mixture was refluxed for 3 days. The reaction mixture was
cooled to room temperature and quenched with methanol. Then the volatiles
were removed under reduced pressure. THF (20 mL) was added to the residue
and polymer was precipitated by slow addition of the solution into 700 mL
of methanol. The third cycle of dissolving-precipitation followed by
freeze-drying gave the polymer as yellow powder.

[0075]For (silole)n(SiMeH)m(SiPhH)0, each 5.5 mmol of
SiMeHCl2 and SiPhHCl2 were slowly added into a THF solution of
silole dianion. In case of (silole-SiH2)m, after addition of
the xylene solution of SiH2Cl2 (11.0 mmol), the resulting
mixture was stirred for 3 days at room temperature instead of refluxing.

[0081]The procedure for synthesizing all germole-silane copolymers was
similar to that for silole-silane copolymers. For
(germole)n(SiMeH)0.5n(SiPhH)0.5n, each 5.0 mmol of
SiMeHCl2 and SiPhHCl2 were added slowly into a THF solution of
germole dianion. The resulting mixture was stirred for 3 days at room
temperature.

[0086]Preparations for other metallole-silane and metallole-germane
copolymers such as tetraalkylmetallole-silane copolymers and
tetraarylmetallole-germane copolymers can be prepared by the above method
described.

Preparation of Poly(tetraphenyl)silole and Poly(tetraphenyl)germole By
Catalytic Dehydrocoupling

[0087]Preparation of polymetallole: 1,1-dihydro-2,3,4,5-tetraphenylsilole
or germole were prepared from the reduction of
1,1-dichloro-2,3,4,5-tetraphenylsilole or germole with 1 mol equiv of
LiAlH4. Additionally, an alternate method to prepare the
dihydrometallole is to add dichlorosilane (25% in xylenes) to an solution
of tetraphenylbutadiene dianion in ether, as described in the literature.
Reaction conditions for preparing the polygermole are the same as those
for polysilole. 1,1-dihydro-2,3,4,5-tetraphenylsilole (1.0 g, 2.59 mmol)
and 1-5 mol % of RhCl(PPh3)3 or Pd(PPh3)4 in toluene
(10 mL) were placed under an Ar atmosphere and degassed through 3
freeze-pump-thaw cycles. The reaction mixture was vigorously refluxed for
72 h. The solution was passed rapidly through a Florisil column and
evaporated to dryness under Ar atmosphere. 1 mL of THF was added to the
reaction mixture and the resulting solution was then poured into 10 mL of
methanol. Poly(tetraphenyl)silole, 1, was obtained as a pale yellow
powder after the third cycle of dissolving-precipitation followed by
freeze-drying. An alternative method for poly(tetraphenyl)silole
preparation is as follows. 1,1-dihydro-2,3,4,5-tetraphenylsilole (1.0 g,
2.59 mmol) and 0.1-0.5 mol % H2PtCl6.xH2O and 2-5 mol
equivalents of allylamine in toluene (10 mL) were vigorously refluxed for
24 hours. The solution was passed through a sintered glass frit and
evaporated to dryness under an Ar atmosphere. Three
dissolving-precipitation cycles with THF and methanol were performed as
stated above to obtain 1. The molecular weights of polymers were obtained
by GPC. 1,1-dihydro-2,3,4,5-tetraphenylsilole with RhCl(PPh3)3,
1: isolated yield=0.81 g, 82%, Mw=4355, Mw/Mn=1.02, determined
by SEC with polystyrene standards; 1,1-dihydro-2,3,4,5-tetraphenylsilole
with Pd(PPh3)4, 1: 0.84 g, 85%, Mw=5638,
Mw/Mn=1.10). 1,1-dihydro-2,3,4,5-tetraphenylgermole with
RhCl(PPh3)3, poly(tetraphenyl)germole: 0.80 g, 81%,
Mw=3936, Mw/Mn=1.01;
1,1-dihydro-2,3,4,5-tetraphenylgermole with Pd(PPh3)4,
poly(tetraphenyl)germole: 0.81 g, 82%, Mw=4221,
Mw/Mn=1.02) 1H NMR (300.133 MHz, CDCl3):
δ=6.30-7.90 (br, m, Ph); 13C(H) NMR (75.403 MHz, CDCl3
(δ=77.00)): δ=124-130 (br, m, Ph), 131-139 (germole carbons).
If less vigorous reflux conditions are used, with the
RhCI(PPh3)3 and Pd(PPh3)4 catalysts, then
corresponding dimers form along with lesser amounts of polymer. The dimer
is less soluble and crystallizes from toluene.

[0091]The high energy of the excited state in the UV luminescent
polysilafluorene offers an increased driving force for electron transfer
to the explosive analyte and improved detection limits by
electrontransfer quenching, which should be applicable for any UV
emitting conjugated organic or inorganic polymer.

[0093]Detection limits of trinitrotoluene (TNT), dinitrotoluene (DNT),
picric acid (PA), 2,2'-dimethyl-2,2'-dinitrobutane (DMNB),
orthomononitrotoluene (OMNT), and paramononitrotoluene (PMNT) were
determined by fluorescence quenching of polysilole, polyDEBsilole,
polygermole, polyDEBgermole, PSF, polyDEBSF, and ExPray.
(DEB=diethynylbenzene.) The emission of PSF is centered in the UV, so
detection limits with a UV camera are expected to be even better than
those determined visually.

[0096]The method of explosives detection is through luminescence quenching
of the metallole-containing polymers by the nitroaromatic analyte. Three
common explosives were tested, Trinitrotoluene (TNT), 2,4-dinitrotoluene
(DNT), and picric acid (PA). Stock solutions of the explosives were
prepared in toluene. Aliquots (1-5 μL) of the stock (containing 5 to
100 ng analyte) were syringed onto either Whatman filter paper or a
CoorsTek® porcelain spot plate and allowed to dry completely. The
spots were between 3 and 10 mm in diameter, producing a surface
concentration of not more than 64 ng/cm2 and not less than 17
ng/cm2. Solutions of the polymers (0.5-1% w:v) were prepared in
acetone (PSi, PGe), 1:1 toluene:acetone (PDEBGe), 2:1 toluene:acetone
(PDEBSi), or toluene (PDEBSF). A thin film of a polymer was applied to
the substrate by spray coating a polymeric solution onto the substrate
and air drying. The coated substrates were placed under a black light to
excite the polymer fluorescence. Dark spots in the film indicate
luminescence quenching of the polymer by the analyte. The process was
carried out for each of the three explosive analytes with each of the six
polymers on both substrates.

Results And Discussion

[0097]Nitroaromatic explosives may be visually detected in nanogram
quantities by fluorescence quenching of photoluminescent
metallole-containing polymers. Detection limits depend on the
nitroaromatic analyte as well as on the polymer used.

[0099]In all cases, the detection limit of the explosives was as low or
lower on the porcelain than on paper, likely because the solvated analyte
may be carried deep into the fibers of the paper during deposition, thus
lowering the surface contamination after solvent evaporation. Less
explosive would be present to visibly quench the thin film of polymer on
the surface. This situation is less pronounced in actuality when
explosives are not deposited via drop-casting from an organic solution,
but handled as the solid. Illumination with a black light
(λex˜360 nm) excites the polymer fluorescence near
490-510 nm for the siloles, 470-500 for germoles. The silafluorene
luminescence, which peaks at 360 nm, is very weak in the visible region,
but it is sufficient for visible quenching.

[0100]FIG. 23 shows a sample black and white images of the luminescence
quenching of three polymers, PSi, PDEBSi, and PGe, by 200, 100, 50, and
10 ng TNT on porcelain plates as observed on a porcelain plate. FIG. 24
shows sample black and white images of the luminescence quenching of
polysilole by each analyte at different surface concentrations.

[0101]The method of detection is through electron-transfer luminescence
quenching of the polymer luminescence by the nitroaromatic analytes.
Consequently, the ability of the polymers to detect the explosives
depends on the oxidizing power of the analytes. The oxidation potentials
of the analytes follow the order TNT>PA>DNT. Both TNT and PA have
three nitro substituents on the aromatic ring which account for their
higher oxidizing potential relative to DNT, which has only two
nitroaromatic substituents. PA has a lower oxidation potential than TNT
due to the electron donating power of the hydroxy substituent. The
molecular structure accounts for the lowest detection limit for TNT,
followed by PA and DNT.

[0102]Luminescence quenching is observed immediately upon illumination.
The polymers are photodegradable, however, and luminescence begins to
fade after a few minutes of continual UV exposure. Nevertheless, these
polymers present an inexpensive and simple means to detect low nanogram
level of nitroaromatic explosives.

[0103]While various embodiments of the present invention have been shown
and described, it should be understood that modifications, substitutions,
and alternatives are apparent to one of ordinary skill in the art. Such
modifications, substitutions, and alternatives can be made without
departing from the spirit and scope of the invention, which should be
determined from the appended claims.

[0104]Various features of the invention are set forth in the appended
claims.

Patent applications by Sarah J Toal, Rockville, MD US

Patent applications by William C Trogler, Del Mar, CA US

Patent applications in class With fluorescence or luminescence

Patent applications in all subclasses With fluorescence or luminescence